After production, analog and radio frequency (RF) blocks undergo extensive calibrations and tests in the manufacturing environment, to check whether their performance is within specification, and to retune components when necessary. The integration of these tests is considered expensive and are thus located off-chip, which limits the testing of the circuit to the manufacturing floor.
Some system manufacturers are considering on-chip self-test and self-tuning, as they promise significant savings in both manufacturing test/tune time and in equipment cost. However, the desire for on-chip testing is often outweighed by the need to keep chip area minimal and the unavailability of excess real estate on the chip.
Thus, there is a continuing need for an on-chip test circuit that overcomes the shortcomings of the prior art.